 Here's another thing. I know a lot of conventional nutritional advice is based on the idea that fat is fattening. We would generally encourage people, therefore, to eat a relatively low fat diet. What does the evidence actually show about whether fat is genuinely fattening and how effective are low fat diets anyway? Let's just start with this. Why do we even believe that fat is fattening? Anyone? We've been told that in the other thought. It's called fat, so that's a little clue. But what else? It's about calories. What about calories? That's right. Fat is twice as many calories as carbohydrates or protein per gram or whatever. That's right. But actually what the evidence shows is if you look at populations, people who eat more fat are not necessarily fat at all. Here's the most important thing. If we're going to recommend low fat diets to people, then surely they should be effective for the purposes of weight loss. Are they? Absolutely not. There's a few studies that have been done that have looked at this, and over, for example, 18 months or so, the average weight loss on a low fat diet is about no weight at all. They are stunningly ineffective for the purposes of weight loss, and that's even when people have apparently induced a calorie deficit. It just doesn't seem to work. So, if we just forget about calories for a moment, just stop thinking about calories and start thinking about something else. How could we potentially explain why some people are carrying more fat than they would like? Well, one thing you need to understand is that fat is at least to some degree under hormonal control. Hormones to some degree influence the storage and the release of fat from our fat cells. Now, there's a few players here that are involved, but there's one important player that I'm going to talk about now, and it is the hormone what? Insulin, that's right. So, insulin basically is a hormone that does a number of different things in the body that basically predispose to fat gain. So, here's a little bit of physiology for you. So, we have fat cells with fat in them, and the aim of the gain, really, is not to have too much fat in our fat cells. So, what is it that insulin does that puts fat in fat cells? Well, fat floating around in the bloodstream is mainly in the form of what are called triglycerides. That's also the form that you tend to store in fat cells. If you can pinch a significant amount of fat, then what you've got basically in your hand is triglyceride. Now, triglyceride cannot get into fat cells. They're large molecules and they need to be disassembled in order to do that. Now, there's a hormone on the surface of fat cells that disassembles triglyceride. And the activity of that hormone is enhanced by insulin. In other words, insulin helps fat to be disassembled so it can gain access into the fat cell. So, that's the first thing. Once it's there, the action of insulin actually provides something that can help fat basically reassemble itself, where it then gets, if you like, semi-stuck in the fat cell. Now, of course, you can release that fat again, but in order to do that, you need the action of an enzyme. And insulin inhibits the action of that enzyme. So, in short, what insulin does is facilitate the uptake of fat into the cells. It makes it more likely to form triglyceride where it's essentially stuck and it can't easily get out of the fat cell. And another thing that it does is inhibit the release of fat, what we call lipolysis. It also, to some degree, not a huge degree, stimulates the production of fat in the liver. So, in summary, you could argue that insulin is a fattening hormone and it has some influence on how much fat we're going to store. The question is, what causes insulin secretion? So, what's the thing that causes most insulin secretion, anyone? Sugar. Yes, sugar. And sugar also comes from starch, as we'll see later, OK? So, essentially, carbohydrate. Protein does cause insulin secretion, but less so than carbohydrate. And, actually, fat, depending on where you look, which bit of the science you look at, has minimal, if any, effect on insulin secretion. So, technically speaking, OK, you could drink liquefied butter all day and not accumulate any fat. Now, that's probably a bit of a stretch, but I'll tell you this. There is a way, OK, of testing whether or not all calories... So, someone earlier mentioned this. Was it you? You said, you know, there's an assumption that all calories have the same effect within the body. Now, one way of testing this would be to take individuals, split them into different groups or a couple of groups, and you'd give them different diets, but you'd keep calories the same. So, for example, you'd feed some people a low-fat, high-carbohydrate diet and you'd feed other people maybe a low-carbohydrate, high-fat diet, right? And if you keep the calories the same and all calories are the same in terms of their effect on fat deposition, then effects on weight should also be the same. Now, there are plenty of studies that show that the effect is the same. There's also a fair amount of studies that don't show that. There's about ten of them. And what they consistently show when they do show a difference is that the diet that is most effective for the purposes of fat loss are the ones that actually contain the most what? Fat, that's exactly right. Now, while that doesn't appear to make sense if you just think all about calories all the time as we're encouraged to, if you think about it in this way and if you think about the critical role potentially of insulin here, then it becomes more explicable. Here's another fundamental problem though. If we eat a very carbohydrate-rich diet we're going to tend to secrete lots and lots of insulin and over a period of time we eventually might become numb to the effects of insulin. In other words, insulin is not doing its job very effectively. Now, the chief function of insulin is to take nutrients out of the bloodstream and put it into your cells. That includes fat. We looked at it earlier, but it also includes sugar. Now, sugar for a lot of people is a basic fuel. They demand on getting sugar into their cells to generate energy. So imagine now your cells, your muscle cells and your brain cells are not able to take up sugar very readily. Now your muscles and your brain are starved of fuel. How might that feel, anyone? Tired, yeah. Physically tired, mentally tired, and here's another thing. If your brain is starved of fuel, don't be too surprised if you are on the hungry side. But here's the other thing. Because sugar is not effectively making its way into the cells, if we eat a lot of foods rich in sugar, so that sugar and starch, then effectively sugar levels might be high and high blood sugar levels are very damaging to the body and it's a reason why diabetics have complications like blindness and kidney disease and the need for amputation. This is not a good situation. Here's another important feature of weight control. It's another hormone and this one's called leptin. Has anyone here heard of leptin? Very good. There's a few health aware people here, very good. So leptin is actually secreted by fat cells. So as we get fatter, the body secretes more leptin and leptin goes to the brain where it has two main effects. It stimulates the metabolism and it makes us less hungry. It suppresses the appetite. This is fantastic because if we were to put on weight and secrete more leptin, then the body is self-regulating and basically telling us not to eat so much by quelling our appetite and also getting us to burn off a bit of that fat. Fantastic. It's all fantastic unless leptin isn't working very well. Either we don't have enough of it for some reason or we're a bit resistant to its effects like we can be resistant to the effects of insulin. Now it appears that leptin resistance in the brain and this is generally viewed as a fundamental problem with weight control with certain individuals is related to a process called inflammation. So if I go up to, I don't know that table and I stub my toe on it, eventually that toe might be a bit sort of red and swollen and painful. That is inflammation. That fundamental pathological process is something called inflammation. What we're talking about here is relatively low-grade inflammation in the body. It may not cause pain, but it appears to be one of the factors that is strongly associated with obesity and possibly through this mechanism. Leptin not working in the brain, so we're a bit hungrier than we should be and our metabolism isn't working quite as well. Now there's also some thought that this issue with leptin resistance might be caused by problems with leptin getting into the brain. And one thing that may block or bar their entry into the brain is a substance called triglycerides. What are these? These are fats. These are fats in the bloodstream and what creates triglycerides? Well a major stimulus for that is our carbohydrate consumption actually. Here's another thing, the spikes in blood sugar. If we eat foods that are very disruptive to blood sugar we'll go through them in depth later on. That also induces inflammation. As does, by the way, certain fats called omega-6 fats that are in things like processed foods, vegetable oils and margarine. Many of these things including the vegetables and the margarine are sold to us as fundamentally healthy. So if you take this all together and you think about this there are a range of reasons why taking a conventional approach to weight loss is basically doomed to failure for the vast majority of people. And it may not be that we're failing. It might be that the approach fails. So let's just summarise this. I know it's depressing but let's just go through this. If you eat less you're almost certainly going to put a dent in your metabolism. And overall it appears that that dent is actually bigger than the dent that you would predict just through weight loss. Reduced energy expenditure because of spontaneously lowered levels of activity. Both animal studies and human studies show when you put them on calorie restricted diets overall they move less. They burn less calories through movement quite spontaneously. You might get nutrient deficiencies. Something might be low calorie but they're very nutritious. These carpet tiles on this stage may well be low calories and may well induce weight loss but they're not very nutritious. The problem is that we might run into problems with nutritional deficiencies that again stifle the metabolism. Hunger. Let's not underestimate the effect of this because this often has a very profound effect on people's mental wellbeing and physical wellbeing. A lot of people find it very difficult to sustain but the other side of this is that if you like avoiding hunger is a prerequisite to success and we'll build on that theme a little bit later on. Raise cortisol levels. That's one thing that happens when people go on calorie reduced diets. The impact there. Cortisol causes fat deposition around the middle generally. If you're eating a lot of carbohydrate and a low fat diet you might also be having a lot of insulin you might also find that it's very difficult for you to set your appetite properly because of the impact that carbohydrates have on blood sugar balance and their innate ability to satisfy the appetite has been shown to be relatively limited. I'll show you some more stuff on that a bit later on. We haven't finished. Increased insulin resistance potentially where effectively the fuel like glucose in the body is not getting into the cells so it's getting tired and hungry. Leptin may not be working very well so now we've got more hunger and less metabolism than we should have and maybe reduce leptin intake into the brain once it's there it doesn't work very well either because we're eating a lot of carbohydrate that's barring its entry through the production of triglycerides. So I would say good luck with that. If you want to use that as your mainstay approach to losing weight and controlling your weight you might think there are possibly better ways of doing that. So a lot of people think well I'm not really bothered about my diet I'm going to do it with exercise. So let's have a look at this for a bit. Here's my question does exercise really promote weight loss? Now when exercise is promoted for weight loss normally what people are being advised to do is to take aerobic exercise so that could be cycling or running jogging, those sorts of things. The idea is you've upped your calorie output haven't you? So if you've upped your calorie output and you're eating the same amount of food you're going to lose weight. What does the actual evidence show though? Forget the theory for a moment so let's imagine you take people you put them on a weight reducing diet that lasts for six months. Let's say they lose 20 pounds for argument's sake not bad at all. Let's say instead of just getting them on their diet you've also asked them to exercise and I'm talking about say 45 minutes of exercise three or four times a week in other words a fair amount of exercise. What is the average amount of weight loss now? It's not 20 pounds it's what does anyone know? What has it to guess? It's what? You're very close. It's 22 pounds. That's the average amount of weight loss that you'd see. So is that the additional weight loss on top of what weight loss you would achieve with diet is just about a kilogram or two pounds. Now let's just think about this for a moment because if you change your diets and lost some weight say over a six month period and you lost I don't know let's call it 10 pounds wouldn't be bad at all.